1. Field of the Invention
The present invention relates to a driving method of an image display apparatus using an electron-emitting device.
2. Description of the Related Art
As a large-screen thin-model display, attention has recently been paid on an image display apparatus with a phosphor excitation of electron beams emitted from an electron source, as is disclosed in “A 10-in. SCE emitter display”, by E. Yamaguchi, et. Al., Journal of SID, Vol. 5, p 345, 1997. The electron beam excitable phosphor display apparatus described above has advantages such that an electron emitting array as a planar electron source can be formed by using a printing technique, a luminous principle same as that in a cathode-ray tube is used since a phosphor is excited to emit light by electrons, and a drive IC with low breakdown voltage can be used since a planar electron source can be driven with a voltage of ten odd volts.
FIG. 17 shows a configuration of an image display apparatus using a planar electron source. An electron-emitting device 12, which is a planar electron source, is formed on a rear plate 6. The electron-emitting device 12 is formed by arranging a conductive film 9 between electrodes 10 and 11. The electron-emitting device 12 is driven by a voltage applied between the electrodes 10 and 11. A microgap is formed on the conductive film 9. Phosphor films 4 of R, G, and B are applied for every pixel on a face plate 3 that is opposite to the rear plate 6. An anode electrode 5 made of aluminum is formed on the phosphor films 4. The portion between both plates 3 and 6 is kept to be vacuum. The electrons emitted from the electron-emitting device 12 are accelerated by the anode voltage to reach the phosphor films 4. The phosphor films 4 are excited to emit light by the energy of the accelerated electrons.
The principle of the luminescence itself of an image display apparatus using a planar electron source is the same as that of a cathode-ray tube. However, in a phosphor display apparatus using a planar electron source, the phosphor layer of the corresponding pixel is excited to emit light by the electrons emitted from the electron source provided for every pixel. The distance between the rear plate and the face plate is several millimeters, which means that the display apparatus is thin. These are great different points from the cathode-ray tube.
FIG. 18 is a plan view showing the configuration of the rear plate. The electron-emitting devices 12 are arranged in a matrix on a glass substrate. The electrode 10 is connected to a scanning wiring 7, while the electrode 11 is connected to a signal wiring 8. Although not shown, an insulating layer for insulating the scanning wiring 7 and the signal wiring 8 from each other is formed between both wirings. In the planar electron source array shown in FIG. 18, all of the conductive film 9, electrodes 10 and 11, scanning wirings 7, signal wirings 8, and insulating layer (not shown) can be formed by printing. Therefore, the formation of a device array on a substrate with large area is facilitated. Accordingly, the planar electron source array has a great prospect as the configuration of a large-screen flat display apparatus.
In FIG. 18, one or the plural scanning wirings 7 are selected by sequentially applying a selection pulse to the scanning wirings 7. On the other hand, drive pulses modulated according to an image signal are applied to each signal wiring 8. Thus, a drive voltage, which is a difference in potential between the selection pulse and the drive pulse, is applied to the electron-emitting device 12 connected to the selected scanning wiring 7. The amount of the electrons emitted from the electron-emitting device 12 can be controlled according to the amplitude and pulse width of the drive voltage. Accordingly, the required amount of electrons can be irradiated to a phosphor, whereby a desired image can be displayed.
The image display apparatus using the planar electron source described above has the features described below. Since the luminescence caused by exciting a phosphor with electron beams having high luminous efficiency is employed, the power consumption is small even if a large screen is used. Since the luminescence of the phosphor is kept in a very short period when the scanning wiring is selected, which means a hold-type display executed in a liquid crystal display (LCD) or a plasma display apparatus (PDP) is not executed, a very natural image can be displayed in displaying a moving image. Further, the image display apparatus described above has a wide viewing angle characteristic without having a viewing angle dependency of a screen brightness like an LCD. Since the planar electron source can be operated with ten-odd volts, it can be driven with a driver IC having low breakdown voltage.
FIG. 19 shows a voltage waveform applied to the electron-emitting device. In FIG. 19, numeral 1 denotes a waveform of a potential Vy of the scanning wiring, and numeral 2 denotes a waveform of a potential Vx of the signal wiring.
In order to drive electron-emitting devices in an optional one line in the matrix, a selection potential Vs is applied to the scanning wiring in the selected line, and at the same time, a non-selection potential Vns is applied to the scanning wirings in the non-selected lines. In synchronism with this, a drive potential Ve for outputting an electron beam is applied to the signal wiring. According to this method, the voltage (drive voltage) of Ve-Vs is applied to the electron-emitting devices in the selected line, while the voltage of Ve-Vns is applied to the electron sources in the non-selected lines. If Ve, Vs, and Vns are set to have a suitable magnitude, the electron beams having a desired intensity must be outputted only from the electron-emitting devices in the selected lines. Further, if the different drive potential Ve is applied to each signal wiring, the electron beam having a different intensity must be outputted from each of the electron-emitting devices in the selected line. Since the response speed of the electron-emitting device is high, the length of the time during when the electron beams are outputted must also be changed if the length of the time during when the drive potential Ve is applied is changed. In FIG. 19, the non-drive potential Vne of the signal wiring is defined as 0 V.
Japanese Patent Application Laid-Open (JP-A) No. 2002-40986 discloses a technique in which an offset voltage having a polarity reverse to that of a drive voltage is applied to an electron-emitting device in the non-selected state in order to reduce a reactive current of the electron-emitting device that is in the non-selected state. Specifically, as shown in FIG. 19, the scanning wiring potential Vy is set to the non-selection potential Vns (0<Vns) in the non-selected state. Since the signal wiring potential Vx becomes 0 V immediately after the selection of the preceding selection lines is completed, an inverse offset state is produced in the non-selected state as shown in FIG. 19. When the scanning wiring potential Vy becomes the selection potential Vs (Vs<0) by which the line is selected, the state of the applied voltage is changed from a reverse polarity to a positive polarity. Further, when the drive potential Ve according to the image signal is applied to the signal wiring, electrons are emitted from the electron-emitting device according to the potential difference (Ve−Vs) between the signal wiring and the scanning wiring. Since the potential difference (Ve−Vns) between the signal wiring and the scanning wiring in the non-selected state is reduced, a leak current of the electron source can be reduced. As a result, the reactive current can be reduced.
JP-A No. 2006-330701 discloses a technique in which the transition between the selection potential and the non-selection potential is performed for 100 nsec to 2 μsec in order to suppress the overshoot and undershoot of the voltage waveform. JP-A No. 2006-330701 discloses a configuration in which the transition period from the selection to the non-selection in the nth line and the transition period from the non-selection to the selection in the (n+1)th line are overlapped with each other.